1. Field of the Invention
The present invention relates to a sheet processing apparatus to perform a post-processing on sheets discharged from an image forming apparatus such as a copier, a printer or a multi function peripheral (MFP).
2. Description of the Related Art
In recent years, among image forming apparatuses, there is one in which a sheet post-processing apparatus is provided to be adjacent to an image forming apparatus main body, so that a post-processing is performed, for example, sheets after image formation are sorted or the sheet are subjected to staple processing. Besides, there is also one in which a sheet bundle is folded in two and is discharged.
JP-A-62-16987 discloses a paper folding apparatus. In this example, there are included a pair of rollers and a folding piece, a sheet is pushed toward a nip side of the paired rollers by the folding piece, and the sheet is folded. Further, there is provided a roller to again press the folded sheet and to additionally fold it.
Besides, JP-A-2004-59304 discloses a sheet processing apparatus including paired folding rollers to fold a sheet and an additional folding roller to additionally fold the sheet. In this example, a mechanism to reduce the noise caused by the additional roller is disclosed.
Further, JP-A-2004-106991 discloses a sheet processing apparatus including paired folding rollers to fold a sheet bundle and an additional folding roller to again press the folded part of the sheet and to additionally fold it. In this example, there is provided control means for determining whether or not additional folding is performed according to the number of sheets.
Besides, JP-A-2005-162345 also discloses a sheet processing apparatus including paired folding rollers to fold a sheet bundle and an additional folding roller to again press the folded part of the sheet and to additionally fold it. In this example, there is disclosed a mechanism to uniformly press the folded part of the sheet by the additional roller.
However, in any of the above-described four examples, the structure is such that the additional folding device is added, and there have been defects that the structure is complicated, and it takes much time to perform the operation of the sheet folding.
The invention provides a sheet processing apparatus including a finisher having a sheet folding mechanism and improved in efficiency of sheet folding operation.